Tascam 48 Dim record and spooling LED - no edit LED

E

ecs787s

New member
Hi all,

Upon fixing the remote connection at the back of my Tascam 48, I accidentally touched some other open leads to the chassis and had a spark. Since, I've noticed that the REC and SPOOLING LEDs are about half lit and the EDIT LED doesn't even turn on! All other features seem to work fine on the deck. I should mention that I've checked all the fuses and power coming out of the Power PCB. Looks like the Control PCB may have an issue somewhere.

Any suggestions would be great! Thanks
 
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It may be that you've just cooked the LEDs. Over-volting them can blow them completely, but it can also burn them out partially (I did this to the 7-segment speed display on my brother's computer 18 years ago)
 
You may have partially damaged the power supply. Check the 15V rail. If you have the manual you can find on the schematics where to find the 15V signal so you can probe it. What may be happening is that the PS got overloaded with the short and can't deliver enough current in some of the rails, likely the 5V or 15V. If that is the problem you may need to change the regulator in the worst case which is not hard to do if you have some electronics experience. I have a tascam 42, wondering if the PS is the same. Maybe it is as the machines are similar, let me check my manual and I can give you some tips on where to look for.
 
fgonza2 said:
You may have partially damaged the power supply. Check the 15V rail. If you have the manual you can find on the schematics where to find the 15V signal so you can probe it. What may be happening is that the PS got overloaded with the short and can't deliver enough current in some of the rails, likely the 5V or 15V.
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You may be right, but I would have thought that if he'd knackered the power supply (or indeed the control PCB) the deck functions themselves would be stuffed. As I read it the only problems are a couple of LED's not the core functionality of the deck.

EDIT: Just to double-check, does EDIT mode actually work?
 
Thanks a lot guys! Yes the edit function does work. All other features do work. Originally the REC button didn't work but then I put in new fuses and all of a sudden it worked. I thought it was weird considering I checked all the fuses for continuity and they all passed.

I do think the 42 and the 48 share many of the same parts including the power supply. I'll check into it. Thanks so much. Oh, if it is just the LEDs can I still even get those? Or will any generic ones work?
 
ecs787s said:
I do think the 42 and the 48 share many of the same parts including the power supply. I'll check into it. Thanks so much. Oh, if it is just the LEDs can I still even get those? Or will any generic ones work?
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I would have thought that any generic ones of the same diameter should work. Don't forget that they're polarised, though. If you put one in backwards it will not be happy.
 
Ok, just checked all voltages coming from Power Supply PCB and all look good. Same with all voltages coming out of Control PCB. Looks like I might in fact just have bad LEDs. Hopefully that is it!

Think I can get some at Radio Shack?
 
ecs787s said:
Think I can get some at Radio Shack?
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I wouldn't know, their UK arm went bankrupt a decade ago and by that point they had stopped selling components.

If it's like the MSR-24, the LED is likely to be an SLP-135B, which is a 3v, 3.0mm red LED so anything matching those specifications should do. You might want to check that on the schematics for your deck if you have them.
 
Update:

Thanks for the replys guys... I now think it isn't blown LEDs. I figure this because after plugging in my RC-71 remote and pressing REC to engage record (which it does) the red LED on it doesn't turn on (on the remote). Now, this remote was not plugged in during any of the shorts, and it did work before. I think the problem resides on the power coming out of the control board onto pins 1, 2, 3 and 5 of P1 on the Control PCB. I'm pretty sure I must have fried something on it. It really isn't that big of a deal since everything on the deck works but the LEDs on the transport. But, it's just the idea of it not working that is killing me! IT MUST WORK!:)

So, do I need to be looking for a visual cue or something that will look blown on that Control PCB? or might it go under the radar and be something were I have to test all the components? What and how would you guys go about testing further? BTW, the Control and Power PCB is the same as the Tascam 42. I found that in my manual.

Thank you again!
 
If there's a driver chip for the LEDs, that may have been damaged.

EDIT: But I'd still think that if the PSU was somehow flakey, it would have messed up the system logic before the LEDs.
 
So, I bought what I thought was the LED Driver IC from Mouser for U18 on the Control PCB and no luck. Now, I'm thinking it might be U3 which doesn't seem to have a replacement part out there...

The part # is MB8243. I didn't seem to see it anywhere in a Google search.
 
Desolder one leg each on R41, R42, R43 and R44 on the Control PCB and measure the resistance of each resistor and report back.
 
Will do, thanks for any help you can give. If I can't get it figured out, no biggie... deck still functions perfectly, just very annoying to me that something is not right!
 
Okay. Let us know.

I believe those resistors are simple voltage dividers to throttle the current that reaches those LED's, and if something shorted it may have pulled too much current through those resistors. I didn't look at the parts list but I assume those are probably 1/6W resistors so it wouldn't take much. Resistors' failure mode is open-circuit. Might have toasted some and nearly toasted others that after passing normal current went into full failure, which would explain why you lost function on some LED's and just experienced dimming and then full failure on others. Don'r recall exactly the progressive symptoms you experienced and I'm too lazy to look, but from memory I seem to recall something died right away, something else presented a slow death and something else just isn't healthy. You wouldn't necessarily be able to see any physical change to the exterior of the resistor if it was toast. You would expect that on a higher voltage circuit but not here. Since that part of the circuit ONLY provides power to the LED's, a failure here won't effect the transport functions which would explain why you are still operating fine. Furthermore, the record LED in the remote taps its power from this same circuit after the resistor, so that would explain why its not working in the remote either. You replaced the driver chip with no positive change, but that doesn't surprise me because those resistors would actually protect the driver chip (depending on the specs of the chip), OR (obviously) even if the driver chip WAS damaged, replacing it won't fix bad resistors.

For future reference, if you can access those components while the deck is powered you could simply start at the effected component, measure voltage (which, if its dead, you won't measure anything), and keep tracing back from the component until you get voltage. At that point you will find the failed component. This will come in handy if you measure your resistors out-of-circuit and they are fine.

You can't measure resistors in-circuit which is why I'm telling you to desolder one leg.

So anyway, let us know what you find.
 
Tascam 48 Control PCB Left.JPGTascam 48 Control PCB Right.JPGTascam 48 Control PCB Schematic.JPG

Ok, after a couple years of not messing with this issue, I've decided to get my butt back in action to finally figure this issue out! I've measured R41-R43 and all check out fine. R44 on the other hand cannot be found!!! I've attached the schematics and a couple of photos of the Control PCB. I, for the life of me cannot find R44. And interesting, I cannot measure a resistance between Pin 12 of U18 and the +15v pin coming into the board. So, where the hell is this little R44!?!! I would love to find it because I think it may be the culprit....
 
Dim Record LED.JPGDim Spool LED.JPG

Here's the condition of the unit... dim Spooling LED when in "Spooling" mode and dim Record LED when in "Recording" mode. The Stop and Edit Button LEDs don't even turn on ever.

Its hard to tell from the photos but both of these LEDs are about half as bright as the others of the same color on the unit.

Thanks for any help y'all!!
 
Upon further investigation, I've found that my model of Control PCB is totally different than that of the blueprint in the manual... in fact the resistor parts in the manual only go up to R183, while its completely visible by this image that I have an R186... I'm thinking there is no longer an R44...
IMG_0595.JPG
 
What I think has happened is that I have a later model 48 and all of my manual/specs/schematics don't reflect the actual hardware I have. Here is the full blueprint of the Control PCB. The real hardware has several more ICs on it as you can see.

IMG_0596.JPG
 
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